1. Field of the Invention
This invention concerns an improved process for C.sub.1 -C.sub.4 alkanol production from synthesis gas under moderate pressure. An improvement in the selectivity of alcohol relative to ester is achieved with promoters, with C.sub.1 -C.sub.4 alkanols making up to 66 wt % of the total liquid product. In addition to improved selectivity for C.sub.1 -C.sub.4 alkanols, there is improved selectivity for ethanol which comprises up to 54% of that fraction.
2. Prior Art
It has long been known that monofunctional alcohols such as methanol, ethanol, etc. can be formed by the reaction of synthesis gas, i.e., a mixture of carbon monoxide and hydrogen at elevated pressures of, for example, up to 1000 atmospheres, and at temperatures of from about 200.degree. to 500.degree. C. or more using as a catalyst a mixture of copper, chromium and zinc oxides. A wide variety of other catalysts have been employed in the reaction of carbon monoxide and hydrogen to yield liquid products containing substantial amounts of monofunctional alcohols as exemplified by methanol, ethanol, propanol, etc. For example, in U.S. Pat. No. 4,013,700 the reaction of carbon monoxide and hydrogen in the presence of a quaternary phosphonium cation and a rhodium carbonyl complex yields a liquid product having a high methanol content. In U.S. Pat. No. 4,014,913 where the same reactants are contacted with a solid catalyst comprising a combination of rhodium and manganese the product formed contains substantial amounts of ethanol and in U.S. Pat. No. 4,197,253 where the reaction of carbon monoxide and hydrogen is conducted in the presence of a rhodium carbonyl complex and a phosphine oxide compound the resulting product contains a high concentration of methanol. Likewise, when the same reactants are contacted with a rhodium carbonyl complex and a copper salt a liquid product containing a substantial amount of methanol is formed.
One serious problem associated with synthesis gas operations in the past has been the non-selectivity of the product distribution since high activity catalysts generally yield a liquid product containing numerous hydrocarbon materials. Thus, complicated recovery schemes are necessary to separate the desired product and the overall yield of the valuable organic products is low. This is a definite need in the art for a process which will produce alkanols, especially ethanol-rich alkanols, with a high degree of selectivity from synthesis gas.
The discovery of a process for making alkanols at moderate pressures, with improved selectivity for ethanol by using a unique catalyst system with a novel promoter would be an advance in the art. The ethanol, methanol, propanol and butanol would be useful as octane enhancers for gasoline blending.